Modern wind turbine rotor blades often being of substantial size and weight require protective measures to protect the blade against overload and fatigue failure during normal use of the wind turbine.
As a consequence wind turbine blades are equipped with different sensor means for sensing strain in the blade. Different sensor solutions have been suggested in order to achieve the necessary precision including strain gauge and optical strain sensors.
Generally the optical sensor solutions do not involving electric cabling which is considered an advantage in relation to protection against damage from lightning strikes and static electricity in the blades.
One known solution includes embedded optical sensors in the inner blade surface in order to achieve the necessary sensor precision but restricts the sensor mounting to the time of blade manufacturing and the sensors are not easily retrofitted if necessary.
Another known solution includes fixing the optical sensor as a unit in a few points on the inner blade surface e.g. with brackets. The fixating allows the sensor to function and at the same time holds it in place. The solution may be somewhat less accurate than for example the embedded sensors e.g. due to precision requirements for each number of points.
It is an object of the present invention to provide solutions for optical sensor means in wind turbines without the abovementioned disadvantages.